In this paper, we examine the properties of a novel kind of nominal ellipsis in Greek, which we call indefinite argument drop (IAD), concentrating on its manifestation in object positions. We argue that syntactically these null objects are present as pro, and we show that semantically they are licensed only by weak DP antecedents (in the sense of Milsark 1974). We compare IAD with NP- internal ellipsis, as attested also in English among many other languages, and show that IAD has distinct syntactic and semantic properties. Finally, we compare our account with a number of proposals regarding null objects in the literature, and show that IAD cannot be reduced to any of these.